Infection due to HIV-1 Subtype C accounts for more than 50% of the global epidemic and nearly all HIV infections in India. Drug resistance is the major cause and consequence of antiretroviral treatment failure. Genotypic resistance assays estimate drug susceptibility and provide guidance to clinicians and policy makers. Though recommended by HIV treatment guidelines in the West, genotyping is rarely performed in public health clinical care in India and other resource limited settings, mainly due to cost and access constraints. This proposal will allow examination of whole blood for transmitted and acquired HIV drug resistance at YRG-CARE in Chennai, India; development of an Indian subtype-C specific point mutation assay that targets the most common drug resistance mutations that occur upon failure of antiretroviral therapy; and validation of the point mutation assay results by Single Genome Sequencing. The Specific Aims are to (1) define prevalence of drug resistance in plasma RNA and proviral DNA in treatment naive and experienced HIV-1 subtype C infected patients at YRG- CARE in Chennai, India. We will test the hypotheses that the detection of drug resistance mutations in proviral DNA predicts transmitted resistance among treatment naive subjects, and virological failure among subjects on treatment; and (2) investigate whether point mutation assays are sensitive and specific in the detection of key drug resistance mutations in plasma RNA and proviral DNA, compared to genotypic gold standards. We will explore the lower limit of detection of minority drug resistance mutations compared to population genotyping and validate quantification of drug resistance mutations by a point mutation assay comparing it to single genome sequencing. These Specific Aims will expand knowledge of the development of HIV drug resistance in India, and allow comparison of HIV RNA and DNA drug resistance mutations by consensus sequencing and by an innovative point mutation assay. This India and US research collaboration will promote technology transfer that has the potential to impact HIV drug resistance surveillance and HIV patient care in India.